The first theorist of these new linguistic developments is none other than the leading Italian poet, Dante Alighieri, who lived from 1265 to 1321. In his De vulgari eloquentia he recognized that Latin, grammatica, was in essence the preserved older form of the Romance languages. He seems to have had as much difficulty in convincing his audience that these ancestral differences were the predictable result of gradual change as Darwin was to find with a different subject matter and timescale, five centuries later.Nor should what we say appear any more strange than to see a young person grown up, whom we do not see grow up: for what moves gradually is not at all recognized by us, and the longer something needs for its change to be recognized the more stable we think it is. So we are not surprised if the opinion of men, who are little distant from brutes, is that a given city has existed always with the same language, since the change in language in a city happens gradually only over a very long succession of time, and the life of men is also, by its very nature, very short....

The italicized portion is Dante Alighieri's analysis.

So then how do we know that a particular language has descended from an older language or that two languages are sister languages, both having evolved from an older language? And the same could be asked of species. How do we know that two species are related and evolved from a common ancestor?

There are parallels in how relationships and ancestry is inferred for languages and species. A comparative analyses of two species may show similarities in body form. For example a structure may be in a same location in the body and will appear in a particular sequence as the body develops from a fetal stage to an adult. This is a particular type of similarity between species and is called a homology and is are used to infer common ancestry, the inference being that the compared species inherited the same structure from a common ancestor and then this structure was modified by evolution in the descendant species. A simple example is the forelimbs in different mammal groups. Some have been modified to fly as in bats, others are paddles to help swim as in whales, while others are adept at manipulating and throwing objects as in a certain primate. Forelimbs occur in the same position in the overall body plan of mammals and follow similar rules of development. They are a homology.

In languages too there are homologies. A common homology is a shared word. Different languages may have similar sounding words to denote the same object... such as the word of mother in say Indo-European languages. That this similar sounding word is due to common ancestry and not due to coincidence is inferred based on whether in the different compared languages the word has a similar sound and has changed following certain known rules of sound change.

One may even infer where a particular language arose and then diversified based on sharing of a word for a particular technology or ecological event which archeology can pinpoint the origin of.

Inferring that similar features are due to common ancestry can become nuanced. Consider a species which splits into many descendant lineages. After diversifying into different species, some of these descendant species may come to evolve the same structure or trait if they encounter similar ecological and selective pressures. In this case the structure itself was not inherited from a common ancestor but evolved independently in these related lineages. An example might be the evolution of feathers in various lineages of the Coelurosuarian dinosaur group. The homology here is not the feathers but shared genes for feathers. It is a deep molecular homology.

This will likely not find a parallel in language evolution. Suppose a people split in to groups and migrate and their languages change. There is less chance that new words for an object they encounter for the first time.. say the different groups see a tiger or a wagon..that the word the groups chose to label these objects will sound the same in the different descendant groups. There are genetic and developmental constraints on evolution. Is there something like a deep molecular homology in languages i.e. the same root word or concept may be used repeatedly by different descendant groups to build similar sounds in daughter languages? Maybe if there is word for a cat like creature in the ancestral language, would a tiger come to be denoted by a word built on the root word for cat or would people simply come up with a completely different sounding word. Is language change is this sense more arbitrary?

Finally, a language may acquire similarities by borrowing words from another language as cultures and people come in to contact with each other. This cross transfer of words is very common in language evolution. English has borrowed french words dating back from the Norman occupation of England in the 11th century. A more ancient example is Sanskrit. The Rig Ved, a collection of hymns in Sanskrit were compiled over a period of hundreds of years around 1800 B.C to 1500 B.C. The younger hymns contain Dravidian words, suggesting that the Indo-Aryan people who composed the Vedas at some point came in contact with Dravidian speakers.

Analogous to word borrowing across languages, genes are occasionally "borrowed" or transferred across species. This transfer of genes between species, known as horizontal gene transfer is more common in prokaryotes, so much so that some biologists think in terms of a web of life rather than a tree of life with discrete branches for the bacterial world. In more complex multicellular organisms horizontal gene transfer is less common but may occur when genes hitchhike on viruses that jump species or due to introgression i.e. when closely related species interbreed.

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ABOUT THIS BLOG

I am a Sedimentary Geologist. On Rapid Uplift I write mostly about topics within the geosciences, but sometimes on biological evolution and environmental issues. I like to travel and in my free time I teach 12 year old kids soccer and rugby.